Method for manufacturing high-strength titanium alloy golf club head part

ABSTRACT

A method for manufacturing a high-strength titanium alloy golf club head part includes making at least one golf club head part with a titanium alloy. The golf club head part is then heated to a temperature higher than a critical temperature of generating martensite and maintained above the critical temperature not more than thirty minutes. The golf club head part is then cooled to a temperature below the critical temperature at a cooling rate higher than 10° C./s. Next, the golf club head part is heated to a heat-treatment temperature higher than 450° C. and maintained at the heat-treatment temperature at least one hour. The golf club head part is then cooled to room temperature. The mechanical characteristics of a golf club head formed by the golf club head part are enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a golf club head part and, more particularly, to a method for manufacturing at least one golf club head part with a high-strength titanium alloy and then processing the golf club head part with several heat-treating processes to enhance the hardness and other mechanical characteristics.

2. Description of Related Art

The primary aim in the golf area is to increase the moment of inertia of the golf clubs for enhancing the striking characteristics. An increase in the overall volume of a golf club is inevitable when the moment of inertia is increased, resulting in a large-size golf club head. However, the overall weight of the golf club head must be kept in a range such that the materials for the golf club head must be light metal with excellent mechanical characteristics and excellent ductility.

Conventional golf clubs are made of stainless steel such as SUS630 or SUS431 (AISI 630 and AISI 431) by casting, forging, or other mechanical processing to form a golf club head part such as a faceplate or club head body. However, the stainless steel has a large density and low strength such that the wall of the resultant golf club head of stainless steel must have a certain thickness to meet the strength requirements. However, in actual use, the striking accuracy and stability are reduced if the golf club head is too heavy, leading to limitation to the volume of the golf club head made of stainless steel.

Researches in making golf club head parts with titanium alloys have been made in an attempt to solve the above problems. U.S. Pat. No. 6,880,222 to Matsunaga discloses a method for manufacturing a golf club head with a titanium alloy. Since the titanium alloy has a density lower than that of the stainless steel, the elastic deforming capability is improved without increasing the overall weight of the golf club head. The overall volume of the golf club head is increased to increase the moment of inertia and the area of striking, such that the striking performance and the striking accuracy are enhanced.

However, the mechanical characteristics such as hardness, tensile strength, and yield strength of titanium alloys are inferior to those of stainless steel such that the mechanical characteristics of the golf club heads made of titanium alloys are inferior to those of the golf club heads made of stainless steel, although the golf club heads made of titanium alloys are lighter. Furthermore, titanium alloy SP700, though having the best mechanical characteristics among currently commercially available titanium alloys, is much expensive than others such as Ti-6Al-4V alloy, Ti-5Al-4V alloy, etc. As a result, the costs for manufacturing golf club heads are largely increased.

A need exists for a novel method for manufacturing golf club head parts in an inexpensive way.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a method for manufacturing a golf club head part by making at least one golf club head part, heating the golf club head part to a temperature higher than a critical temperature and maintaining the golf club head part above the critical temperature for a period of time, cooling the golf club head part at an appropriate cooling rate, and heat-treating the golf club head part, enhancing the mechanical characteristics of the titanium alloy.

The secondary object of the present invention is to provide a method for manufacturing a golf club head part whose mechanical characteristics are enhanced by heating, cooling, and heat treating such that the method of the present invention can be utilized to manufacture large-size golf club heads with high moment of inertia.

A method for manufacturing a high-strength titanium alloy golf club head part according to the preferred teachings of the present invention includes making at least one golf club head part with a titanium alloy. The golf club head part is then heated to a temperature higher than a critical temperature of generating martensite and maintained above the critical temperature not more than thirty minutes. The golf club head part is then cooled to a temperature below the critical temperature at a cooling rate higher than 10° C./s. Next, the golf club head part is heated to a heat-treatment temperature higher than 450° C. and maintained at the heat-treatment temperature for 1-8 hours. The golf club head part is then cooled to room temperature. The mechanical characteristics of a golf club head formed by the golf club head part are enhanced.

Other objects, advantages and novel features of this invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flowchart illustrating a method for manufacturing a high-strength titanium alloy golf club head part according to the preferred teachings of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a method for manufacturing a high-strength titanium alloy golf club head part according to the preferred teachings of the present invention includes making at least one golf club head part (such as a faceplate or a portion of a golf club head body) with a titanium alloy; heating the golf club head part to a temperature higher than a critical temperature of generating martensite and maintaining the golf club head part above the critical temperature for a period of time; rapidly cooling the golf club head part to a temperature below the critical temperature at an appropriate cooling rate; heating the golf club head part to a heat-treatment temperature and maintaining at the heat-treatment temperature for a period of time; and cooling the golf club head part to room temperature.

Specifically, a first step S1 of the method for manufacturing the high-strength golf club head part according to the preferred teachings of the present invention includes making at least one golf club head part with a titanium alloy. Since the mechanical characteristics of an α-type titanium alloy are inferior to those of an α-β-type titanium alloy and can not be enhanced by heat treatment and since a β-type titanium alloy is inferior to the α-β-type titanium alloy in the heat-resistant properties and anti-oxidation properties and has a larger specific weight, an α-β-type titanium alloy is utilized in the method according to the preferred teachings of the present invention to make the golf club head part. Examples of such an α-β-type titanium alloy include Ti-2Al-1.5Mn alloy, Ti-3Al-1.5Mn alloy, Ti-3Al-2V alloy, Ti-6Al-4V alloy, and Ti-5Al-1Fe alloy. Preferably, the α-β-type titanium alloy is Ti-6Al-4V (containing 6% of aluminum by weight and 4% of vanadium by weight, with the remaining portion being titanium) to allow easy casting, forging, and/or other mechanical processing procedures to process the α-β-type titanium alloy to a desired shape of the golf club head part.

Since titanium (with a density of 4.51 g/cm³), aluminum (with a density of 2.70 g/cm³), manganese (with a density of 7.20 g/cm³), and vanadium (with a density of 5.79 g/cm³) are the main components of the α-β-type titanium alloy, the density of the α-β-type titanium alloy is obviously lower than that of stainless steel (such as SUS630 with a density of 7.80 g/cm³). Thus, when utilizing the α-β-type titanium alloy to manufacture a golf club head, the overall volume of the golf club head can be largely increased while maintaining the overall weight of the golf club head in a certain range.

A second step S2 of the method according to the preferred teachings of the present invention includes heating the golf club head part to a temperature higher than a critical temperature of generating martensite and maintaining the golf club head part above the critical temperature for a period of time. The critical temperature is lower than a β-phase transformation temperature of the α-β-type titanium alloy. The α-β-type titanium alloy gradually turns into martensite when the temperature is higher than the critical temperature. The temperature of the α-β-type titanium alloy is maintained higher than the critical temperature for a period of time so that the β phase in the α-β-type titanium alloy gradually turns into α′ phase, forming a martensite structure consisting of tiny, unstable α phase and α′ phase. The critical temperature and the temperature-maintaining period are dependent on the material of the α-β-type titanium alloy. Since the critical temperature of Ti-6Al-4V alloy utilized in this embodiment is 800° C., the temperature of Ti-6Al-4V is preferably kept in a range of 800° C. to 980° C. and, most preferably, in a range of 890° C. to 950° C. Furthermore, the temperature of Ti-6Al-4V alloy is preferably maintained not more than thirty minutes.

If the temperature of the α-β-type titanium alloy is lower than the critical temperature or if the temperature-maintaining period is too short, the β phase in the α-β-type titanium alloy can not efficiently turn into α′ phase such that the mechanical characteristics and hardness of the α-β-type titanium alloy are reduced after subsequent procedures. On the other hand, if the temperature of the α-β-type titanium alloy is higher than the critical temperature and higher than an upper temperature limit or if the temperature-maintaining period is too long, the crystalline grains of martensite will be too coarse, leading to deterioration of the mechanical characteristics including plasticity and toughness.

A third step S3 of the method according to the preferred teachings of the present invention includes cooling the golf club head part to a temperature below the critical temperature by a coolant at an appropriate cooling rate. Suitable coolants include liquefied nitrogen, water, mineral oils, plant oils or other fluids. The golf club head part is cooled to a temperature below the critical temperature and below a heat-treatment temperature in the subsequent step. In this embodiment, the golf club head is cooled to nearly room temperature. During this cooling procedure, the cooling rate is appropriately adjusted according to the material and shape of the golf club head part. Furthermore, different α-β-type titanium alloys have different critical cooling rates such that the cooling rate in the third step S3 must be higher than the critical cooling rate of the golf club head part.

If the cooling rate is too slow, complete martensite structure can not be obtained in the α-β-type titanium alloy such that the α-β-type titanium alloy can not reach the required hardness. On the other hand, if the cooling rate is too fast, great structural stress and great heat stress will be generated in the α-β-type titanium alloy during transformation of the martensite structure, and the golf club head part will break or even be damaged. Thus, the cooling rate of the golf club head part is preferably higher than 10° C./s.

A fourth step S4 of the method according to the preferred teachings of the present invention includes heating the golf club head part to a heat-treatment temperature lower than the critical temperature of the α-β-type titanium alloy and maintaining the golf club head part at the heat-treatment temperature for a predetermined period of time that is preferably between 1 and 8 fours and, more preferably, between 4 and 6 fours. Finally, the golf club head part is cooled naturally or by a coolant to room temperature. The heat-treatment temperature for Ti-6Al-4V alloy is preferably in a range of 450° C. to 600° C. and, more preferably, in a range of 520° C. to 560° C.

Since residual stress and unstable martensite structures exist in the α-β-type titanium alloy after the third step S3 (the cooling procedure), the atomic energy in the α-β-type titanium alloy is increased by raising the temperature of the α-β-type titanium alloy again such that the atoms in the α-β-type titanium alloy are realigned and reorganized to eliminate the residual stress, to stabilize the size of the golf club head part, and to enhance the plasticity.

The second, third, and fourth steps S2, S3, and S4 are aging processes for transforming the α′ phase into a stable structure in which α phase and β phase coexist. Thus, the mechanical characteristics of the golf club head part can be effectively enhanced while maintaining suitable elongation and plasticity. Table 1 shows the mechanical characteristics of a golf club head part without aging and golf club heads subjected to the second step S2 of the method according to the preferred teachings of the present invention. Apparently, the mechanical characteristics of the golf club heads subjected to the second step S2 of the method according to the preferred teachings of the present invention are superior to those of golf club heads without aging.

TABLE 1 tensile strength yield elongation hardness processing (ksi) strength (ksi) (ksi) (HRC) without aging 143.1 125.6 21.98 33.4 heated to 950° C. and 163.2 148.8 5.1 36.3 maintained for 20 minutes heated to 930° C. and 159.4 146.9 11.74 40.3 maintained for 30 minutes

The method according to the preferred teachings of the present invention can be utilized to manufacture different golf club head parts that can be assembled by suitable methods to form a golf club head having a hardness in a range of HRC 34 to HRC 50, a tensile strength in a range of 150 ksi to 170 ksi, and a yield strength in a range of 135 ksi to 155 ksi. Suitable methods for assembling the golf club head parts include brazing, bonding, inserting, pressing, screwing, or other welding methods such as argon welding, laser welding, electronic beam welding, and plasma welding. However, the method according to the preferred teachings of the present invention can be utilized to manufacture a golf club head formed by a single golf club head part.

As mentioned above, conventional golf club head parts made of stainless steel or titanium alloys without aging are too heavy and have low strength and, thus, can not be utilized to manufacture large-size golf club heads with excellent mechanical characteristics and high hardness. By contrast, by utilizing the method according to the preferred teachings of the present invention, golf club head parts with excellent mechanical characteristics and high hardness can be manufactured and assembled to form large-size golf club heads with high moment of inertia.

While the principles of this invention have been disclosed in connection with specific embodiments, it should be understood by those skilled in the art that these descriptions are not intended to limit the scope of the invention, and that any modification and variation without departing the spirit of the invention is intended to be covered by the scope of this invention defined only by the appended claims. 

1. A method for manufacturing a high-strength titanium alloy golf club head part comprising the steps of: making at least one golf club head part with a titanium alloy; heating said at least one golf club head part to a first temperature higher than a critical temperature of generating martensite and maintaining the golf club head part above the critical temperature not more than thirty minutes; cooling said at least one golf club head part to a second temperature below the critical temperature at a cooling rate higher than 10° C./s; heating said at least one golf club head part to a heat-treatment temperature higher than 450° C. and maintaining at the heat-treatment temperature for 1-8 hours; and cooling said at least one golf club head part to room temperature.
 2. The method as claimed in claim 1, further comprising: assembling said at least one golf club head part into a golf club head having a hardness in a range of HRC 34 to HRC 50, a tensile strength in a range of 150 ksi to 170 ksi, and a yield strength in a range of 135 ksi to 155 ksi.
 3. The method as claimed in claim 1, wherein the titanium alloy is an α-β-type titanium alloy.
 4. The method as claimed in claim 3, wherein the critical temperature of generating martensite of said at least one golf club head part is lower than a β-phase transformation temperature of the α-β-type titanium alloy.
 5. The method as claimed in claim 3, wherein the α-β-type titanium alloy is Ti-2Al-1.5Mn alloy, Ti-3Al-1.5Mn alloy, Ti-3Al-2V alloy, Ti-6Al-4V alloy, or Ti-5Al-1Fe alloy.
 6. The method as claimed in claim 5, wherein the critical temperature of said at least one golf club head part made of Ti-6Al-4V alloy is in a range of 800° C. to 980° C.
 7. The method as claimed in claim 1, wherein cooling said at least one golf club head part including cooling said at least one golf club head with a coolant selected from a group consisting of liquefied nitrogen, water, mineral oils, and plant oils.
 8. The method as claimed in claim 5, wherein the heat-treatment temperature of said at least one golf club head part made of Ti-6Al-4V alloy is in a range of 450° C. to 600° C.
 9. A golf club head part made of high-strength titanium alloy, with the high-strength titanium alloy being made by a method comprising the steps of: heating an α-β-type titanium alloy to a temperature higher than a critical temperature of generating martensite; maintaining the temperature of the α-β-type titanium alloy above the critical temperature not more than thirty minutes; cooling the α-β-type titanium alloy to room temperature at a cooling rate higher than 10° C./s; heating the α-β-type titanium alloy to a heat-treatment temperature higher than 450° C. and maintaining the α-β-type titanium alloy at the heat-treatment temperature for at least one hour; and cooling the α-β-type titanium alloy to room temperature.
 10. The golf club head part as claimed in claim 9, wherein the α-β-type titanium alloy has a hardness in a range of HRC 34 to HRC 50, a tensile strength in a range of 150 ksi to 170 ksi, and a yield strength in a range of 135 ksi to 155 ksi.
 11. The golf club head part as claimed in claim 9, wherein the critical temperature of generating martensite of the α-β-type titanium alloy is lower than a α-phase transformation temperature of the α-β-type titanium alloy.
 12. The golf club hear part as claimed in claim 9, wherein the α-β-type titanium alloy is Ti-2A-1.5Mn alloy, Ti-3Al-1.5Mn alloy, Ti-3Al-2V alloy, Ti-6Al-4V alloy, or Ti-5Al-1Fe alloy.
 13. The golf club head part as claimed in claim 12, wherein the Ti-6Al-4V alloy has a critical temperature in a range of 800° C. to 980° C.
 14. The golf club head part as claimed in claim 9, wherein the α-β-type titanium alloy is cooled with a coolant selected from a group consisting of liquefied nitrogen, water, mineral oils, and plant oils.
 15. The golf club head part as claimed in claim 12, wherein the heat-treatment temperature of the Ti-6Al-4V alloy is in a range of 450° C. to 600° C. 